A frequency synthesizer may generally be described as an electronic system for generating any of a range of frequencies from a reference signal having a particular frequency. Frequency synthesizers may be found in many different kinds of devices, such as, radio transceivers, mobile telephones or cellular phones, radio base stations (RBSs), satellite transceivers, GPS systems, etc.
In for example a mobile radio application, a signal to be used when transmitting and receiving data is conventionally generated by a frequency synthesizer comprising a phase-locked loop (PLL). A PLL frequency synthesizer may for example have a reference signal with a certain frequency as input, and a programmable counter which may generate a comparison signal by dividing an output signal outputted from the PLL frequency synthesizer. The output signal from the PLL frequency synthesizer may be an output signal outputted from an oscillator also comprised in the PLL frequency synthesizer. The PLL frequency synthesizer may further include a phase comparator for comparing the phase of the input reference signal with the phase of the comparison signal from the programmable counter and produce an output signal in dependence of this phase difference. From this output signal, a control signal (e.g. a tuning voltage) may be generated and used as input to the oscillator in order for the oscillator to generate and output an output signal having a specific frequency and specific noise characteristics, that is, the output signal outputted from the PLL synthesizer.
However, when the PLL and the oscillator comprised in the PLL are designed for applications which have high requirements on the noise performance of the output signal as opposed to other applications with low requirements on the noise performance of the output signal, the PLL and the oscillator are designed using different technologies. Examples of applications with high requirements on the noise performance of the output signal are network units or nodes, such as, e.g. base stations (for example, Radio Base Stations (RBSs)). Examples of applications with low requirements on the noise performance of the output signal are terminal units, such as, e.g. mobile telephone applications. The PLL is conventionally designed as an integrated circuit (IC), while the oscillator is designed using discrete electrical components, such as, e.g. resistors, capacitors, inductors, etc. This is inter alia because implementing the oscillator on an integrated circuit would result in that the signal-to-noise ratio of the output signal outputted from the PLL would not fulfil the high requirements on the noise performance of many existing and new emerging applications on the market today.
Using different technologies such as an integrated PLL circuit and a discrete oscillator to form a frequency synthesizer, however, does not enable a compact solution from a miniaturization perspective, as well as it does not provide a particularly cost effective solution from a manufacturing standpoint. These are factors to consider in contemporary design of various telecommunication applications and wireless devices, etc.